Protuberantia Menti (Chin)

Chin development results from the combination of several features. One is the trigonum mentale, a triangular eminence on the anterior face of the mandible. Ontogenetically, this structure results from the fusion of several elements (a central tuber symphyseos and two lateral tuberculia lateralia). Above it, a more or less marked incurvation (incurvatio mandibulae) is visible in lateral view. Lateral depressions (fossae mentales) between the trigonum and the canine sockets are present in children and may or may not persist in adults. A well-developed chin is also associated with a mandibular symphyseal profile (i.e., the section of the mandible by the mid-plane) that is vertically-oriented or receding supero-posteriorly. It is often considered a unique derived trait of recent Homo sapiens ("anatomically modern humans"). However, it is notable that Middle Pleistocene and Neandertal specimens can display some level of incurvation and a tuber symphyseos. Conversely, early Homo sapiens can display a still moderately salient trigonum mentale, with a symphyseal angle still receding infero-posteriorly. The development of the bony chin has been interpreted as resulting from 1) the reduction of the alveolar part (bearing the teeth) relative to the basal part of the mandible, 2) complex developmental interactions among facial components during recent human evolution, and/or 3) a biomechanical response to these new conditions.